A Scary New World Order

With China and other emerging markets gaining importance, the world could be in for a nasty shock when their economies sour. A discordant note in the jobs report.

It used to be said that when the U.S. sneezed, the rest of the world caught a cold. That was because the American economy was by far the world's biggest, and relatively small ripples here could result in big waves when they washed up on shores abroad.

But, according to some new measures, America may be about to cede its position as the world's biggest economy to China, perhaps as early as this year. Not only would that be of enormous...